This invention relates to a robotic manipulator more particularly to such manipulators constructed to control the movement of an end-effector in three degrees of freedom.
Many attempts have been made to design mechanisms for the three degree of freedom (3-DOF) control of a moveable end-effector. The applications have been diverse, from electronic component assemblies to realistic force-reflecting master hand controllers. The following provide examples of such three degree of freedom manipulators.
SCARA Robot (U.S. Pat. No. 4,693,666)
One of the oldest mechanisms for 3-DOF planar manipulation is the SCARA robot. It is commonly used in tasks such as automated circuit board stuffing. SCARA robots are serial mechanisms having parallel actuation axes that allow translation of an end-effector in space as well as rotation of the end-effector about an axis parallel to the actuation axes. Typical arrangements involve rotational shoulder and elbow actuators that position a two-axis wrist that rotates and translates a gripper along an axis parallel to the shoulder and elbow axes. Typically the proximal actuators carry the distal ones. The mass of the distal actuators, as well as the mass of the stiff structure required to carry them, limit achievable accelerations. In order to alleviate this problem, four-bar linkages or belt transmissions have been used to place both the shoulder and elbow actuator in the robot base. The robot moving mass is substantially reduced by this technique. However, the rotational and translational gripper actuators still have to be carried by the robot arm.
Substrate Feeder (U.S. Pat. No. 5,713,717)
The substrate feeder provides 3-DOF planar motion through parallel actuation. It can move quickly due to its parallel actuation.
Parallel Manipulator (U.S. Pat. No. 5,539,291)
This device performs 3-DOF translation/rotation manipulations using a parallel structure but operates over a cylindrical surface rather than in the plane. No orientation of the gripper in order to perform an operation such as bolt tightening is available with this structure.
4-DOF Manipulator (U.S. Pat. No. 5,673,595)
The 4-DOF Manipulator uses 2 five-bar linkages in parallel to provide spatial positioning as well as one degree of rotation. This invention describes a pair of links connected to each other at their distal ends by a single passive rotational joint to form a variable angle vertex. The proximal ends of the links are connected via universal joints to planar translational movers such as five-bar linkages. The planar translational movers translate and orient the pair of links in a plane. The vertex angle and therefore its height is defined by the distance between the planar translational movers. Although the translational mobility of this mechanism is essentially that of a SCARA robot, the end-effector of this mechanism does not have a fixed orientation with respect to a working plane and the mechanism does not provide unlimited rotation range about an axis. As well, there are many passive joints defining the mechanism vertex and hence the end-effector position, leading to play and therefore inaccuracies in its position.
It is therefore an object of the present invention to provide an improved manipulator providing three degree-of-freedom planar translation and orientation to an end-effector while minimizing the disadvantages discussed above with respect to known manipulators.
It is an object of the invention to provide a manipulator wherein all of the actuators are attached to the base, resulting in low mass, which allows for high speed and high acceleration operation.
The primary objective to provide a manipulator with actuators fixedly attached to the base and having unlimited rotation range.
A secondary object is to provide a manipulator with the ability to alter its angular motion transmission ratio through the inclusion of an extensible link.
An object is to produce a device having fewer geometric design parameters, thus easing its design for a specific application.
A further object of the present invention is to provide a manipulator that permits simplified control computations by allowing analytical solutions of both the inverse and forward kinematics which avoids the need for complex control calculations that plague many parallel devices.
Broadly the present invention relates to a three degree of freedom manipulator comprising a base, a pair of off set substantially parallel rotary joints, a crankshaft mounted in said pair of rotary joints, said crankshaft having an interconnecting portion extending between said pair of rotary joints, a pair of joint moving means one to independently move each of said rotary joints in a plane perpendicular to the rotary axes of said joints, said pair of joint moving means each being mounted on said base and drive means on said base for independently and controllably driving each of said joint moving means to independently move each of said rotary joints.
Preferably each of said joint moving means comprises a five-bar linkage composed of a pair of proximal links, each said proximal link pivotally connected at one end to said base for pivotal movement on a first pivotal axis, all of said first pivotal axes for said pair of joint moving means being substantially parallel to each other and a pair of distal links each of which is pivotally connected on a second pivotal axis to its link of said pair of proximal links, said second pivotal axes being spaced from and parallel to said first pivotal axes, said pair of distal links of one of said pair of joint moving means having one said pair of rotary joints adjacent to their ends remote from said their second pivotal axis and said pair of distal links of the other of said pair of joint moving means having the other of said pair of rotary joints adjacent to their ends remote from said their second pivotal axis, axes of rotation of said pivotal joints and of said pair of rotary joints being substantially parallel.
Preferably said drive means includes a separate drive means for each of said proximal links of each of said pair of joint moving means around its said first pivotal axis.
Preferably said three degree of freedom manipulator will further include an end effector, and said crankshaft will include an offsetting portion extending laterally beyond one of said pair of rotary joints, said end effector being mounted on said offsetting portion.
Preferably said interconnecting portion includes an extendable section, which may be changed in length, to change the spacing between said first and second rotational axes.
Preferably said extensible section is formed by an axially extendable link.
Preferably said extensible section is formed by means of a pair of links interconnected by a further rotational joint permitting rotation about an axis of rotation parallel to said axes of rotation of said pivotal joints and of said pair of rotary joints.
Preferably each of said joint moving means and said drive means comprises at least one prismatic actuator means for moving each of said rotary joints.
Preferably each of said joint moving means comprises a pair of interacting prismatic actuators.